1. Field of the Invention
The present invention relates to a lens-fitted photo film unit with a built-in flash device wherein flash device elements, including a flash charge switch and a flash projector, are integrated into a unit on a flash circuit board. The present invention also relates to a flash device for use in a lens-fitted photo film unit or a camera.
2. Background Arts
A lens-fitted photo film unit is widely known as a device, which is provided with a simple exposure mechanism and is loaded with an unexposed photo film cartridge in the factory, so that anyone can enjoy photography without bothering about loading and rewinding the film. Hereinafter, the lensfitted photo film unit will be referred to as a film unit.
There are many film units on the market that have a flash device incorporated therein to make it possible to photograph in the dark. The film units mostly have a unit body that is constituted of a rear cover and a basic portion holding a roll of unexposed photo filmstrip therebetween, an exposure unit that has a taking lens, a shutter mechanism and so forth as an integrated assembly and is attached to a front middle area of the basic portion, a flash unit that constitutes the built-in flash device and is attached to the front of the basic portion on one side of the exposure unit, and a front cover for covering the front of the basic portion so as to hold the exposure unit and the flash unit onto the basic portion. For making a flash photography, it is necessary to charge a main capacitor of the flash device up to a predetermined voltage. Therefore, it is usual to turn on the flash charge switch to charge the main capacitor prior to the flash photography.
The flash charge switch is turned on by operating a charging operation member. There are various charging operation members: a push button type is formed integrally with the front cover and bent down resiliently to turn on the flash charge switch, a pull-up type is pulled up to turn the flash charge switch on, and a sliding type is slidable between an ON position and an OFF position. The sliding type charge operation member is either mounted to the front cover through a sliding guide member, or held between the front cover and the flash circuit board.
Of the film unit where the charge operation member is mounted to the front cover in a slidable fashion, the front cover is complicated in construction, and it needs another process for mounting the flash charge member to the front cover prior to an assembling process of the unit body. This type is therefore disadvantageous in view of production efficiency and cost. The film where the charge operation member is sandwiched between the front cover and the flash circuit board is more advantageous in view of production efficiency and cost, but it is necessary to position the charge operation member stably in the assembling process of the unit body. Forming a guide member for the charge operation member on the basic portion might be possible but difficult because it goes against the requirement of making the film unit thinner.
The flash circuit is classified into two types: one continues charging only while the flash charge switch is ON, and the other starts charging once the flash charge switch is turned on for a moment, continues charging even after the flash charge switch is turned off, and stops charging automatically when the charge voltage reaches a predetermined level. The latter type will be called an automatic charge-stopping type. A flash device where the flash charge switch is kept in the ON position by keeping pressing a push button type charge operation member is the simplest in mechanical and electrical construction, and thus requires the lowest production cost. However, keeping pressing the charge operation member to the end of charging is obviously inconvenient. A flash device which continues charging till the charge voltage reaches the predetermined level once the flash charge switch is turned on by pressing a push button type charge operation member for a moment is improved in workability and is effective to reduce a waste of electric power. However, the automatic charge-stopping type flash circuit needs more circuit elements and a higher production cost. According to its circuit construction, the automatic charge-stopping type flash circuit automatically starts charging again after the flashing, so that it is impossible to make a non-flash photography in succession to a flash photography.
On the other hand, the flash device using a sliding type or a pull-up type charge operation member has an advantage that it continues charging once the charge operation member is set to the ON position, and that the flashing can be interrupted by resetting the charge operation member to the OFF position. However, since the charging operation does not stop unless the user resets the charge operation member to the OFF position, the battery would run drawn to disable flashing any further if the user forget to turn off the flash charge switch.
Meanwhile, if a user should drop a film unit with a built-in flash device in the sea, sea water will ooze into the film unit. Because sea water is conductive, if the main capacitor of the flash device is charged at that time, the charged current can leak through the sea water. If the user touches the film unit with bare hand in that condition, the user will get an electric shock as the current flows through the sea water and the hand.